PC Processors

[yup259]

Hi,

i did some research about mainboard chipsets (b550 x570) and I want to understand the performance impact of the mb chipset cpu lane being either pci3 or 4.

Can someone explain how pci3 limits the cpu compared to pci4 and, if that even makes sense, name a cpu that would mark the breakpoint between pci3 and 4 resulting in equal performance and then pci4 being necessary for more performant cpus? I know that pci4 is faster but I want to know how and when it makes a difference. As an example, if I have a 10gb lan port or a 1gb port, I could say 10gb is faster but as long as my isp only offers speeds less than 1gb (and there's no internal network traffic) the difference would never matter.

so let's say I put a 5600x on a b550 mb or a x570, how much does the performance differ in % and is the difference in general or only in specific cases like if the cpu hits 100% usage? Is the eventual performance gap higher for a better cpu like 5800x3d? Would it be bad to put a high end cpu like 5800x3d on a b550 in terms of limitations due to pci3 or put differently, does the 5800x3d require a x570?

thanks for any help

[yup259]

Hello, thank you for the answer. The compatibility is one thing but my question was more about the difference between pci3 and pci4 lanes from mb chipset to cpu. The 5800x3d is compatible with b550 and x570. A b550 board connects the gpu with x16 pci4 (that no card of today can saturate) and a ssd with x4 pci4 that is about enough for the fastest ssds right now (around 7.x gb). Since ram is connected directly to the cpu without pci, my question is where do I notice a bandwidth and latency difference resulting from the either pci3 or pci4 lane between chipset and cpu. What is left to connect is onboard usb and Ethernet and ?? Which all won't even use the pci3 bandwith. What's the impact of a pci4 chipset lane?

thank you for any reply

[ryzen_type_r · Accepted solution]

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@yup259 wrote:

Since ram is connected directly to the cpu without pci, my question is where do I notice a bandwidth and latency difference resulting from the either pci3 or pci4 lane between chipset and cpu. What is left to connect is onboard usb and Ethernet and ?? Which all won't even use the pci3 bandwith. What's the impact of a pci4 chipset lane?

Primarily you would only really see a difference if you have a lot of I/O devices and use them simultaneously.

The 5xxx series SoC allows for 4 10Gbps SuperSpeed USB ports, and 24 lanes of PCIe 4.0.  Of the 24 lanes, 16 are typically routed to a PCIe slot for graphics, 4 for motherboard chipset connectivity, and 4 for a single NVMe.  Motherboard manufacturers are given flexibility in how exactly they route the lanes and the USB though.  It is possible, for example, for a motherboard to split the 4 lanes for NVMe into 2 x2 NVMe slots.  And they can connect USB hubs to the SoC USB ports to increase the number of physical ports (this doesn't increase bandwidth, just the number of ports)

Any additional I/O would be off the chipset and ultimately limited by that 4 lane link to the CPU.  The X570 thus would have double the CPU to chipset bandwidth than the B550, since the X570 will run those 4 lanes at 4.0 speeds, and the B550 is limited to 3.0 speeds.

Motherboards almost always have an additional USB controller off the chipset, Ethernet (maybe dual, or even 2.5Gbps), WiFi, and any additional NVMe slots will connect through the chipset.  And of course, anything you connect to the PCIe slots on the motherboard will ultimately share that 4 lane link to the CPU.

So if your use case requires a lot of I/O connectivity, then the X570 is better suited for you.

Note that in theory, an external chipset isn't even required for a functional Ryzen PC.  The CPU itself has all the connectivity for a fully functional PC, it would just have limited (but still sufficient) connectivity.  The X570 chipset is actually just a Ryzen SoC in a separate package.

[yup259]

Hello

 thank you for the detailed explanation. It helped me a lot!!